Malaria is a common and still increasing infectious disease in many countries. Malaria affects the red blood cells in a complex system of propagation of the mosquito Anopheles. Sporozoites invade the red blood cells (erythrocytes) and eventually rapture the red blood cells. The effect of malaria is, among others, the destruction of the red blood cells causing anemia in the patient.
Today, microscopy is the gold standard for determination of malaria burden and the effect of treatment thereof. The microscopy methods used are so-called thin layer and thick layer methods. The thin layer method is defined by a single layer of red blood cells, whereas the thick layer method uses hemolyzed red blood cells corresponding to 10-20 layers of red blood cells.
Thin layer microscopy by a skilled operator can morphologically identify the parasite to the species level and determine the percentage of the red blood cells that are infected. The number of such red blood cells containing parasites, as seen as “black dots”, in relation to the total number of red blood cells is calculated and used as degree of malaria or malaria burden.
The thick layer method is considered to be the more sensitive method. A defined layer or volume of blood is hemolyzed and the free parasites in a certain area or portion of the blood sample are counted. The disadvantage of this method is that red blood cells cannot be counted due to the hemolyzation. In order to get a measure or estimate of the malaria burden and to follow the effect of any malaria treatment, it is necessary to determine the concentration of the red blood cells.
The above described so-called thin or thick layer methods for determining the degree of the malaria burden require usage of a microscope and a skillful user. In addition, both methods are furthermore quite time consuming.
Malaria diagnosis can furthermore be done by immunological point-of-care (POC) rapid in vitro diagnostic tests. These tests are more costly and are generally not able to directly give information of the degree of malaria burden. Hence, the microscopy methods are the preferred methods in those countries where malaria is most frequent.
WO 2011/123070 discloses determination of the percentage of the red blood cells in a blood sample that are infected by malaria parasites. The disclosed technique uses a flow cytometer together with nucleic acid dyes that react with DNA or react with DNA and RNA and antibodies coupled to a fluorophore and capable of selectively binding to a marker present on leukocytes.
The prior art method of determining a parasitemia value in WO 2011/123070 is marred by a rather complex set-up requiring several chemicals and cumbersome detection equipment.
Hence, there is a need for an efficient solution to determine, preferably automatically determine, parasitemia values for patients infected by malaria parasites and that can be used outside of clinical laboratories.